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AD7390 датащи(PDF) 10 Page - Analog Devices |
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AD7390 датащи(HTML) 10 Page - Analog Devices |
10 / 12 page AD7390/AD7391 REV. 0 –10– RESET (CLR) PIN Forcing the CLR pin low will set the DAC register to all zeros and the DAC output voltage will be zero volts. The reset func- tion is useful for setting the DAC outputs to zero at power-up or after a power supply interruption. Test systems and motor con- trollers are two of many applications which benefit from power- ing up to a known state. The external reset pulse can be generated by the microprocessor’s power-on RESET signal, by an output from the microprocessor, or by an external resistor and capacitor. CLR has a Schmitt trigger input which results in a clean reset function when using external resistor/capacitor generated pulses. The CLR input overrides other logic inputs, specifically LD. However, LD should be set high before CLR goes high. If CLR is kept low, then the contents of the shift reg- ister will be transferred to the DAC register as soon as CLR re- turns high. See the Control-Logic Truth Table I. UNIPOLAR OUTPUT OPERATION This is the basic mode of operation for the AD7390. As shown in Figure 26, the AD7390 has been designed to drive loads as low as 5 k Ω in parallel with 100 pF. The code table for this op- eration is shown in Table IV. +2.7V to +5.5V 0.1 µF VOUT CLR SDI CLK LD 3 2 1 4 GND REF VDD AD7390 7 6 5 10 µF µC RS RL ≥ 5kΩ CL ≤ 100pF EXT REF 0.01 µF R Figure 26. AD7390 Unipolar Output Operation Table IV. AD7390 Unipolar Code Table Hexadecimal Decimal Output Number Number Voltage (V) in DAC Register in DAC Register VREF = 2.5 V FFF 4095 2.4994 801 2049 1.2506 800 2048 1.2500 7FF 2047 1.2494 000 0 0 The circuit can be configured with an external reference plus power supply, or powered from a single dedicated regulator or ref- erence depending on the application performance requirements. BIPOLAR OUTPUT OPERATION Although the AD7391 has been designed for single-supply op- eration, the output can be easily configured for bipolar opera- tion. A typical circuit is shown in Figure 27. This circuit uses a clean regulated 5 V supply for power, which also provides the circuit’s reference voltage. Since the AD7391 output span swings from ground to very near 5 V, it is necessary to choose an external amplifier with a common-mode input voltage range that extends to its positive supply rail. The micropower con- sumption OP196 has been designed just for this purpose and re- sults in only 50 microamps of maximum current consumption. Connection of the equal valued 470 k Ω resistors results in a dif- ferential amplifier mode of operation with a voltage gain of two, which results in a circuit output span of ten volts, that is, 5 V to 5 V. As the DAC is programmed with zero-code 000H to midscale 200H to full-scale 3FFH, the circuit output voltage VO is set at 5 V, 0 V and 5 V (minus 1 LSB). The output volt- age VO is coded in offset binary according to Equation 4. Equation 4 VO = 5 1 512 D where D is the decimal code loaded in the AD7391 DAC regis- ter. Note that the LSB step size is 10/1024 = 10 mV. This cir- cuit has been optimized for micropower consumption including the 470 k Ω gain setting resistors, which should have low tem- perature coefficients to maintain accuracy and matching (prefer- ably the same material, such as metal film). If better stability is required the power supply could be substituted with a precision reference voltage such as the low dropout REF195, which can easily supply the circuit’s 162 µA of current, and still provide additional power for the load connected to VO. The micropower REF195 is guaranteed to source 10 mA output drive current, but only consumes 50 µA internally. If higher resolution is re- quired, the AD7390 can be used with the addition of two more bits of data inserted into the software coding, which would re- sult in a 2.5 mV LSB step size. Table V shows examples of nominal output voltages VO provided by the Bipolar Operation circuit application. DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY OP196 BIPOLAR OUTPUT SWING 5V 5V VO < 50 µA 5V AD7391 VOUT GND REF VDD C 470k Ω 470k Ω 5V < 100 µA ISY < 162µA Figure 27. Bipolar Output Operation Table V. Bipolar Code Table Hexadecimal Decimal Analog Number Number Output In DAC Register in DAC Register Voltage (V) 3FF 1023 4.9902 201 513 0.0097 200 512 0.0000 1FF 511 -0.0097 000 0 -5.0000 |
Аналогичный номер детали - AD7390 |
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Аналогичное описание - AD7390 |
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